The present invention relates to a method and apparatus for removing old asphalt from a pavement surface and reconditioning it so that it is suitable for use in repaving.
It is well known that asphalt flows in response to applied pressure and in time oxidizes and develops bumps, ruts, cracks and other defects. Originally, grinders were used to break down the old asphaltic surface which was then picked up and transported by truck to a processing plant, reprocessed, and the reprocessed asphalt transported back and reapplied in a known way. More recently equipment has been developed to recycle the old asphalt on site. U.S. Pat. No. 3,843,274 issued Oct. 22, 1974 to Gutman et al., discloses a vehicle having an infra red heater to first heat the asphalt, a rotating cutter for lifting the heated asphalt up a ramp and a pugmill for pulverizing the lifted asphalt. Finally, a spreader screw distributes the pulverized asphalt across the road surface and a heating and vibrating means levels and compacts the asphalt. The limited heating capacity of Gutman et al combined with the low thermal conductivity of asphalt allows its cutter to cut through only a thin layer of asphalt unless it were to cut through unsoftened asphalt. Proper reconditioning of an asphalt surface requires that it strip at least 2 inches off of the old surface. Thus, miltiple passes are required with a machine such as that disclosed in Gutman et al.
U.S. Pat. No. 3,970,404 issued to Benedetti discloses a method of achieving a greater depth of penetration in the heating step by interrupting the heating steps with heat transfer steps in which radiant heat is not applied allowing heat to soak in and the surface temperature to lower. A greater depth of heating of the order of 1 inch or more is achieved.
U.S. Pat. No. 4,226,552 issued Oct. 7, 1980 to Moench discloses the use of 7 different vehicles to perform a series of treatments on old asphaltic pavement to render it suitable for reuse on site. First, the pavement is heated and then scarified to break it up into a loose aggregate asphalt mixture lying on a lower hard asphaltic surface. A second vehicle heats the broken up aggregate and underlying hard surface and then breaks up the pavement down to a further depth. The broken up asphalt is graded into a narrow row, picked up and heated, mixed with a reconditioning agent, pulverized and spread over the road surface. A major problem with Moench is the need to heat the hard asphalt with an overlying layer of broken up previously heated asphalt. Much of the radiant energy is absorbed by the overlying broken up layer and so transfer of radiant energy to the underlying unbroken asphalt is substantially reduced from what it would otherwise be without a covering of loose asphalt.
U.S. Pat. No. 4,335,975 issued to Schoelkopf on June 22, 1982 discloses a machine and method by which old pavement is heated, broken up by a tearing up beam or blade and ground into a grain type structure by two semi-worm blades and screeding and accumulation blades. Fresh asphalt is then poured over the softened broken up old asphalt and compacted. Since old asphalt loses ingredients such as resins on oxidation it is necessary to add these to old asphalt to replace the lost ingredients. It is also necessary to heat the old mixture so that these added resins resolublize the asphaltenes in the asphalt. The absence of heating, the addition of rejuvenants and pulverizing prior to reapplying the old asphalt to the road surface in the Schoelkopf process means the old asphalt is not adequately restored prior to reuse by that process. U.S. Pat. No. 4,534,674 issued on Aug. 13, 1985 to Cutter discloses a process similar to that of Schoelkopf.
U.S. Pat. No. 4,545,700 issued Oct. 8, 1985 to Yates discloses a process of sequentially heating and milling an asphalt road surface using lateral collection chutes to guide milled material to the rear of the machine. An additive is added prior to the last milling step and mixed in with the aggregate which is then reapplied. Yates uses a somewhat elaborate system of collection chutes to contain and guide removed material to the rear of the machine.